svm: fix layered build

Author: zapster

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/fs/runtimeinit/FileSystemProviderRuntimeInitSupport.java

@@ -27,6 +27,7 @@
 
 import java.nio.file.FileSystem;
 import java.nio.file.spi.FileSystemProvider;
+import java.util.Objects;
 
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
@@ -73,13 +74,21 @@ final class Target_java_io_DefaultFileSystem_RunTime {
  * {@code JDKInitializationFeature}.
  */
 class DefaultFileSystemHolder {
-    static final Target_java_io_FileSystem_RunTime FS = Target_java_io_DefaultFileSystem_RunTime.getFileSystem();
+    static final Target_java_io_FileSystem_RunTime FS;
+    static {
+        if (SubstrateUtil.HOSTED) {
+            // unused - layered images might want to initialize during image build
+            FS = null;
+        } else {
+            FS = Target_java_io_DefaultFileSystem_RunTime.getFileSystem();
+        }
+    }
 }
 
 class DefaultFileSystemAccessor {
     @SuppressWarnings("unused")
     static Target_java_io_FileSystem_RunTime get() {
-        return DefaultFileSystemHolder.FS;
+        return Objects.requireNonNull(DefaultFileSystemHolder.FS);
     }
 }
 
@@ -96,7 +105,16 @@ final class Target_sun_nio_fs_DefaultFileSystemProvider_RunTime {
  * {@code JDKInitializationFeature}.
  */
 class SunNioFsDefaultFileSystemHolder {
-    static final FileSystem FS = Target_sun_nio_fs_DefaultFileSystemProvider_RunTime.theFileSystem();
+    static final FileSystem FS;
+
+    static {
+        if (SubstrateUtil.HOSTED) {
+            // unused - layered images might want to initialize during image build
+            FS = null;
+        } else {
+            FS = Target_sun_nio_fs_DefaultFileSystemProvider_RunTime.theFileSystem();
+        }
+    }
 }
 
 @TargetClass(className = "sun.nio.fs.UnixFileSystem", onlyWith = JDKInitializedAtRunTime.class)
@@ -115,7 +133,7 @@ final class Target_sun_nio_fs_UnixPath_RunTime {
 @SuppressWarnings("unused")
 class UnixFileSystemAccessor {
     static Target_sun_nio_fs_UnixFileSystem_RunTime get(Target_sun_nio_fs_UnixPath_RunTime that) {
-        return SubstrateUtil.cast(SunNioFsDefaultFileSystemHolder.FS, Target_sun_nio_fs_UnixFileSystem_RunTime.class);
+        return Objects.requireNonNull(SubstrateUtil.cast(SunNioFsDefaultFileSystemHolder.FS, Target_sun_nio_fs_UnixFileSystem_RunTime.class));
     }
 
     static void set(Target_sun_nio_fs_UnixPath_RunTime that, Target_sun_nio_fs_UnixFileSystem_RunTime value) {
@@ -142,7 +160,7 @@ final class Target_sun_nio_fs_WindowsPath_RunTime {
 @SuppressWarnings("unused")
 class WindowsFileSystemAccessor {
     static Target_sun_nio_fs_WindowsFileSystem_RunTime get(Target_sun_nio_fs_WindowsPath_RunTime that) {
-        return SubstrateUtil.cast(SunNioFsDefaultFileSystemHolder.FS, Target_sun_nio_fs_WindowsFileSystem_RunTime.class);
+        return Objects.requireNonNull(SubstrateUtil.cast(SunNioFsDefaultFileSystemHolder.FS, Target_sun_nio_fs_WindowsFileSystem_RunTime.class));
     }
 
     static void set(Target_sun_nio_fs_WindowsPath_RunTime that, Target_sun_nio_fs_WindowsFileSystem_RunTime value) {